Mordenite zeolite membrane and method for producing the same

ABSTRACT

A mordenite (MOR) zeolite membrane is formed on a porous substrate and dominantly oriented in a specific crystalline direction. A method for producing a mordenite (MOR) zeolite membrane includes the steps of: immersing a porous substrate in a gel of raw material which contains zeolite constitution elements and contains 40-400 of SiO 2 /Al 2 O 3  in molar ratio, 10-120 of H 2 O/Na 2 O in molar ratio, and 10-40 of H 2 O/SiO 2  in molar ratio, and subjecting the gel in the presence of the porous substrate to hydrothermal synthesis at 150° C. or more to make zeolite crystallized to form a membrane thereof. The MOR zeolite membrane is oriented in a specific crystalline direction.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0001] The present invention is directed to an MOR zeolite membrane which is dominantly oriented in a specific crystalline direction and a method for producing the membrane. Zeolite has a frame structure of crystalline aluminosilicate and a mesh-like structure composed of fine pores of a minute uniform diameter. Thus, zeolite is used as a molecule sieve or a catalyst.

[0002] For example, JP-A-7-330326 discloses a zeolite membrane which is formed on a single crystal substrate of an oxide, a semiconductor or a metal and oriented in a specific crystalline direction, and zeolite membranes of A type, Y type and the like are given in the examples.

[0003] In addition, WO92/13631 discloses zeolite membranes comprising an oriented single layer of ZSM-5 (MFI), an A type, a Y type, an X type and the like. WO97/25272 discloses an MFI zeolite membrane oriented along the b axis and a method for producing the membrane. Further, WO96/01683 discloses an MFI zeolite membrane oriented along the a axis and the c axis and the method for producing the membrane.

[0004] However, a mordenite (MOR) zeolite membrane oriented in a specific crystalline direction is not known till now. An MOR zeolite membrane is superior in acid resistance in comparison with zeolite membranes of an A type, a Y type and the like, and it is extremely useful if such an MOR zeolite membrane can be obtained.

SUMMARY OF THE INVENTION

[0005] The present invention has been made in view of such a conventional problem and aims to provide an MOR zeolite membrane dominantly oriented in a specific crystallization direction and a method for producing the membrane. That is, according to the present invention, there is provided a mordenite (MOR) zeolite membrane formed on a porous substrate and dominantly oriented in a specific crystalline direction.

[0006] According to the present invention, there is further provided a method for producing a mordenite (MOR) zeolite membrane comprising the steps of:

[0007] immersing a porous substrate in a gel of raw material which contains zeolite constitution elements and contains 40-400 of SiO₂/Al₂O₃ in molar ratio, 10-120 of H₂O/Na₂O in a molar ratio, and 10-40 of H₂O/SiO₂ in molar ratio, and subjecting the gel in the presence of the porous substrate to hydrothermal synthesis at 150° C. or more to make zeolite crystallized to form a membrane thereof.

[0008] In the above, it is preferable that the porous substrate is disposed in a reaction vessel so that a surface on which a membrane is formed becomes perpendicular, and that the gel of the raw material contains SiO₂/Al₂O₃ of 100-400 in molar ratio, H₂O/Na₂O of 10-100 in molar ratio, and H₂ 0/SiO₂ of 10-30 in molar ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1(a) is an SEM photograph showing a crystal structure of a surface of the membrane obtained in Example 1, and

[0010]FIG. 1(b) is an SEM photograph showing a crystal structure of a section of the membrane obtained in Example 1.

[0011]FIG. 2(a) is an SEM photograph showing a crystal structure of a surface of the membrane, and

[0012]FIG. 2(b) is an SEM photograph showing a crystal structure of a section of the membrane obtained in Example 2.

[0013]FIG. 3 is an SEM photograph showing a crystal structure of a section of the membrane obtained in Example 3.

[0014]FIG. 4 is a graph showing an X-ray diffraction pattern of the membrane obtained in Example 3.

[0015]FIG. 5 is an SEM photograph showing a crystal structure of a section of the membrane obtained in example 4.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention is hereinbelow described in detail.

[0017] The present invention is a mordenite (MOR) zeolite membrane dominantly oriented in a specific crystalline direction and formed on a porous substrate.

[0018] Such an MOR zeolite membrane can be produced by immersing a porous substrate in a gel of raw material containing zeolite constitution elements having a specific composition and subjecting the gel in the presence of the porous substrate to hydrothermal synthesis at 150° C. or more.

[0019] In the above MOR zeolite membrane, the crystalline direction is not particularly limited and, it is oriented along any one of the a axis, b axis and c axis. This MOR zeolite membrane has a high ratio of silica and is superior in acid resistance in comparison with an A-type zeolite membrane and a Y-type zeolite membrane, and therefore can be applied for use requiring acid resistance in fields of molecule sieves and catalysts.

[0020] Next, a method for producing the above MOR zeolite membrane is described.

[0021] As a raw material, there is used a raw material sol constituted by a simple substance including silicon, aluminum, and an alkali metal, which are zeolite constitution elements, a compound thereof, and the like.

[0022] It is important that the gel of raw material has a composition range of 40-400 of SiO₂/Al₂O₃ in molar ratio, 10-120 of H₂O/Na₂O in molar ratio, and 10-40 of H₂O/SiO₂ in molar ratio. In the case that a raw material has a composition outside the about range, an MOR zeolite membrane dominantly oriented in a specific crystalline direction may not be obtained. As a composition range of the raw materials, it is more preferable that the molar ratio of SiO₂/Al₂O₃ is 100-400, the molar ratio of H₂O/Na₂O is 10-100, and the molar ratio of H₂O/SiO₂ is 10-30.

[0023] Next, a porous substrate is immersed in the raw-material gel having the above composition range. In the present invention, not a generally-used dense substrate but a porous substrate is employed. A material for a porous substrate is not limited, and various kinds of materials such as ceramics, metals and the like may be used. There is exemplified, as a non-limited example, a substrate made of a ceramic of general oxide such as alumina, zirconia, titania, silica, or the like; a compound oxide such as silicazirconia, silicatitania, or the like; and a substrate made of a metal such as iron, stainless steel, copper, tantalum, or the like.

[0024] Membrane formation by crystallization is performed by subjecting a gel of raw material for zeolite to hydrothermal synthesis with putting a porous substrate having a seed crystal applied thereon in an autoclave. The important thing here is to perform hydrothermal synthesis at a temperature of 150° C. or more. If a temperature of hydrothermal synthesis is below 150° C., an MOR zeolite membrane dominantly oriented in a specific crystalline direction may not be produced. It is required that a temperature of hydrothermal synthesis is 150° C. or more for securing an orientation property. It is more preferable that a temperature for hydrothermal synthesis is within 165-175° C., and it is particularly preferable that the temperature is around 180° C.

[0025] In addition, it is preferable in the present inventive process to dispose a porous substrate in a reaction vessel so that a surface of said substrate on which a membrane is formed becomes perpendicular. The expression “dispose the substrate perpendicularly” means that the substrate is disposed in a reaction vessel in such a manner that the substrate surface on which membrane is formed is placed perpendicularly to the ground. Thus, by performing hydrothermal synthesis with a porous substrate being disposed perpendicularly in a reaction vessel, a crystallized MOR zeolite membrane dominantly oriented along the b axis or the c axis may be produced. In the case that a porous substrate is disposed in a reaction vessel so that a surface of the substrate on which a membrane is formed becomes horizontal to the ground, one may obtain an MOR zeolite membrane having only a lower layer being oriented in a specific crystalline direction, with a not-oriented upper layer.

[0026] Incidentally, a so-called seeding step, in which a seed crystal is applied beforehand upon crystallizing by using hydrothermal synthesis is not required in producing an MOR zeolite membrane of the present invention. However, it is preferable to perform a seeding step because a dense zeolite membrane may be obtained, and as a consequence a membrane having a good separation performance may be obtained.

[0027] The present invention is hereinbelow described with reference to Examples and Comparative Examples in more detail. However, the present invention is not limited thereto.

EXAMPLE 1

[0028] b-axis Oriented MOR Zeolite Membrane

[0029] 0.425 g of sodium aluminate was mixed with sodium hydroxide solution (7.26 g NaOH+28.8 g H₂O) to give a mixture, and the mixture was sufficiently stirred at room temperature (20° C.). 72 g of colloidal silica (30 wt % SiO₂+0.6 wt % Na₂O) was added to the resultant, and it was sufficiently mixed at 50° C. till a transparent solution was obtained. The resultant raw material gel had a molar ratio of 10Na₂O: 0.15Al₂O₃: 36SiO₂: 440H₂O.

[0030] The surface of a porous alumina tube (10 mm of outer diameter, 60 mm long) having a fine pore diameter of 0.1 μm was washed, and a commercial mordenite seed crystal (molar ratio: SiO₂/Al₂O₃=10.2) was applied on the surface of the substrate by a dip method. Then, they were dried by 100° C. for 15 minutes. The prepared raw material gel solution was put in an autoclave, and the porous alumina tube was perpendicularly sunk in the gel by the use of a Teflon support stand. Then, the autoclave was closed. Subsequently, hydrothermal synthesis was performed at 180° C. for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface thereof was sufficiently washed with distilled water. Then, the resultant product was dried at 100° C.

[0031] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was a mordenite (MOR) zeolite membrane dominantly oriented along the b axis. FIG. 1(a) is an SEM photograph showing a crystal structure of a surface of the membrane, and FIG. 1(b) is an SEM photograph showing a crystal structure of a section of the membrane.

COMPARATIVE EXAMPLE 1

[0032] The same procedure as in Example 1 was repeated until the hydrothermal synthesis, which was performed at 100° C. for 2 weeks. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface of the substrate was sufficiently washed with distilled water. Then, the resultant product was dried at 100° C.

[0033] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, in which no X-rays diffraction peak was recognized, and the membrane was confirmed to be amorphous.

EXAMPLE 2

[0034] c-axis Oriented MOR Zeolite Membrane

[0035] 3.7045 g of aluminum sulfuric anhydride was sufficiently mixed with sodium hydroxide solution (12.595 g NaOH+40 g H₂O) at room temperature to obtain a solution. A mixture of 80 g of colloidal silica and 192 g of water was sufficiently mixed with the above-obtained solution for 1 hour. The formed raw material gel had a molar ratio of 0.38 Na₂O: 0.025Al₂O₃: SiO₂: 40H₂O.

[0036] The surface of a porous alumina tube (10 mm of outer diameter, 60 mm long) having a fine pore diameter of 0.1 μm was washed, and a commercial mordenite seed crystal (molar ratio: SiO₂/Al₂O₃=10.2) was applied on the surface by a slurry coat method. Then, the tube was dried at 100° C. for 15 minutes. The above gel was put in an autoclave, and the porous alumina tube was sunk in the gel by the use of a Teflon support stand. The autoclave was closed, and hydrothermal synthesis was performed at 180° C. for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface was sufficiently washed with distilled water. Then, the resultant product was dried by 100° C.

[0037] The membrane formed on the substrate tube was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was a mordenite (MOR) zeolite membrane dominantly oriented along the c axis which was oriented in parallel with a substrate of the porous alumina tube. FIG. 2(a) is an SEM photograph showing a crystal structure of a surface of the membrane, and FIG. 2(b) is an SEM photograph showing a crystal structure of a section of the membrane.

COMPARATIVE EXAMPLE 2

[0038] 2.277 g of aluminum sulfuric anhydrite was sufficiently mixed with sodium hydroxide solution (0.23 g NaOH+6 g H₂O) at room temperature to a solution. 20 g of colloidal silica was sufficiently mixed with the solution for 2 hours. The formed raw material gel had a molar ratio of 3Na₂O: Al₂O₃: 20Si₂O: 200H₂O.

[0039] The surface of a porous alumina tube (a diameter of 10 mm, 60 mm long) having a fine pore diameter of 0.1 μm was washed, and a commercial mordenite seed crystal (molar ratio: SiO₂/Al₂O₃=10.2) was applied on the surface by a slurry coat method. Then, the tube was dried at 100° C. for 15 minutes. The above gel solution was put in an autoclave, and the porous alumina tube was sunk perpendicularly by the use of a Teflon support stand. The autoclave was closed, and hydrothermal synthesis was performed at 180° C. for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface was sufficiently washed with distilled water. Then, the resultant product was dried at 100° C.

[0040] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, in which no X-ray diffraction peak was recognized, and the membrane was confirmed to be amorphous.

COMPARATIVE EXAMPLE 3

[0041] 1.129 g of aluminum sulfuric anhydride were sufficiently mixed with sodium hydroxide solution (3.84 g NaOH+78 g H₂O) at room temperature to obtain a solution. 20 g of colloidal silica was sufficiently mixed with the resultant solution for 1 hour. The formed raw materials gel had a molar ratio of 0.48Na₂O: 0.033Al₂O₃: SiO₂: 50H₂O.

[0042] The surface of a porous alumina tube (10 mm of outer diameter, 60 mm long) having a fine pore diameter of 0.1 μm was washed, and a commercial mordenite seed crystal (molar ratio: SiO₂/Al₂O₃=10.2) was applied on the surface by a slurry coat method. Then, the tube was dried at 100° C. for 15 minutes. The above gel solution was put in an autoclave, and a porous alumina tube was sunk perpendicularly in the gel by the use of a Teflon support stand. The autoclave was closed, and hydrothermal synthesis was performed at 180° C. for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface was sufficiently washed with distilled water. Then, the resultant product was dried at 100° C.

[0043] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, in which no X-ray diffraction peak was recognized, and the membrane was confirmed to be amorphous.

EXAMPLE 3

[0044] c-axis Oriented MOR Zeolite Membrane

[0045] A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 2 except that a raw-material gel had a molar ratio of 0.28 Na₂O: 0.0042 Al₂O₃: SiO₂: 12.2H₂O and that a hydrothermal synthesis was performed at 180° C. for 2 days.

[0046] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was a mordenite (MOR) zeolite membrane dominantly oriented along the c axis which was oriented in parallel with a substrate of the porous alumina tube. FIG. 3 is an SEM photograph showing a crystal structure of a section of the membrane, and FIG. 4 is a graph showing an X-ray diffraction pattern.

COMPARATIVE EXAMPLE 4

[0047] A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 3 except that hydrothermal synthesis was performed at 100° C.

[0048] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was not oriented in a specific direction and had random orientation though crystallization was recognized.

COMPARATIVE EXAMPLE 5

[0049] A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 3 except that hydrothermal synthesis was performed at 140° C.

[0050] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was not oriented in a specific direction and had random orientation though crystallization was recognized.

COMPARATIVE EXAMPLE 6

[0051] A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 2 except that a raw material gel had a molar ratio of 0.15Na₂O: 0.05Al₂O₃: SiO₂: 10H₂O. After being cooled, the porous alumina tube was taken out, and it was found to find out that no membrane was formed on the porous alumina tube.

EXAMPLE 4

[0052] A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 3 except that porous alumina tube was sunk horizontally in an autoclave and that hydrothermal synthesis was performed at 180° C. for 24 hours.

[0053] The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that a membrane was not oriented in a layer on the upper side and dominantly oriented along c axis only in a layer on the lower side which was near the porous alumina tube substrate side though crystallization was recognized. FIG. 5 is an SEM photograph showing a crystal structure of a section of the membrane.

[0054] As discussed above, according to the present invention, there can be provided an MOR zeolite membrane oriented in a specific crystalline direction and a preferable method for producing the membrane. 

What is claimed is:
 1. A mordenite (MOR) zeolite membrane formed on a porous substrate and dominantly oriented in a specific crystalline direction.
 2. A method for producing a mordenite (MOR) zeolite membrane comprising the steps of: immersing a porous substrate in a gel of raw material which contains zeolite constitution elements and contains 40-400 of SiO₂/Al₂O₃ in molar ratio, 10-120 of H₂O/Na₂O in a molar ratio, and 10-40 of H₂O/SiO₂ in a molar ratio, and subjecting the gel in the presence of the porous substrate to hydrothermal synthesis at 150° C. or more to make zeolite crystallized to form a membrane thereof.
 3. A method as defined in claim 2 , wherein the porous substrate is disposed in a reaction vessel so that a surface of the substrate on which a membrane is formed becomes perpendicular to the reaction vessel.
 4. A method as defined in claim 2 or 3 , wherein as a composition range of the raw materials, the molar ratio of SiO₂/Al₂O₃ is 100-400, the molar ratio of H₂O/Na₂O is 10-100, and the molar ratio of H₂O/SiO₂ is 10-30. 